Machining of equipment or components requires very sturdy restrains and hold downs of workpieces. Tolerances on machined surfaces can be very small, requiring not only no movement of the workpiece, but minimum stress and strain on the workpiece during machining. Since machining operations, by removing material, inherently produce high stress, one of the goals of holding devices is to quickly transfer these stresses from the workpiece to the machine tool bed or other support.
Many holding devices are available. The most common are vises. These are precision tools which clamp the workpiece between two long jaws which are secured to a vise structure which is attached to the machine tool bed. Jaws may have interchangeable faces to adapt to different workpiece shapes. Jaw are also designed to clamp and not protrude beyond surfaces not being machined into the plane of the surface being machined. The two long opposing jaw faces are parallel planes and require workpiece to present two parallel clamp planes for proper alignment.
This approach presents difficulties during machining of billets. Multiple cuts on each surface to be machined may be required. Alignment and restraint of billet by vise jaws gripping rough, as received billets or stock surfaces do not allow heavy cuts, alignment or final machining operations. This frequently requires multiple rough machining on long noncritical clamp surfaces just to mate with and allow long vise jaws to properly grip and position workpiece. These vises also require significant space on the machine tool bed.
These limitations are especially troublesome on numerically controlled machining equipment and/or for precision machining operations. Multiple cuts on clamping surfaces require delay and expense of unclamping, repositioning, alignment, and reclamping. Long precision reference surfaces must be established for final critical surface machining. Alignment and operation of multiple vises can be especially time consuming. These limitations are compounded when multiple workpieces are machined in a single operation.